One of the features added in the iOS 4.3 update is the ability to tether to your iPhone via wifi in addition to the USB and bluetooth tethering that's been in iOS since 3.0. I understand the use case for wifi tethering (multiple devices, non-computers like iPads, etc) and I understand the use case for USB (keep the device powered so battery doesn't run down).

What circumstances would bluetooth tethering be preferred to wifi and USB?

3 Answers
3

I would imagine that Bluetooth tethering over WiFi or USB would be a matter of convenience, or if a device doesn't have the appropriate ports for USB. Another thought, MiWi OnDemand (jailbreak only), when being used between multiple iOS devices, will connect to a paired iPhone for internet connectivity over Bluetooth only when needed. I suppose that Bluetooth is more on-demand whereas using your phone as a constant WiFi access point would drain the battery considerably faster.

When I'm without AC power, I will generally use Bluetooth over USB. This is because my Mac's battery gets drained while charging the iPhone's battery. Between the Mac's own needs and the iPhone, the battery drains too quickly. When I have AC, this isn't an issue.